1. Field of the Invention
This invention relates to a process of gapping a slide fastener chain, more particularly of providing element-free zones at predetermined intervals on and along a longitudinal edge of a continuous slide fastener stringer carrying therealong a series of coupling elements formed by injection or extrusion molding and interconnected by a connecting string. The invention further relates to an apparatus for carrying this process into practice.
2. Prior Art
A typical form of slide fastener stringers to which the invention is applied comprises, as shown in FIGS. 15 and 16 of the accompanying drawings, a support tape carrying along one of its longitudinal edges a multiplicity of discrete coupling elements interconnected by a connecting string and secured in place by sewn seams, each of the coupling elements having a coupling head portion and upper and lower leg portions mounted astride the tape edge. During the course of finishing such elongate fastener stringer which is usually dyed, it is the common practice to remove certain numbers of the coupling elements to provide "space" or element-free zones at predetermined intervals on the support tape which are utilized subsequently for threading sliders through the tape and for attachment of upper and lower end stop members, the stringer being thereafter cut across the element-free zones into individual fastener lengths.
There have heretofore been proposed numerous means of gapping a slide fastener chain, a typical prior art example of which is introduced in U.S. Pat. No. 4,131,223 wherein the gapping operation is automated with use of coacting cutters adapted to sever the coupling elements and another set of cutters to cut off the connecting string which interconnects adjacent individual elements on a slide fastener chain having two stringers in coupled condition. The coacting cutters are disposed in vertically offset positions such that the support tape is forced to assume substantially "S"-letter like flexed posture as the cutters sever the elements and further advance toward each other until severed element debris are pulled apart. This arrangement has a drawback in that the cutters would impair the tape and often exert undue stresses upon and sometimes cut the sewing threads which are securing the elements to the tape. Should this happen, the sewing threads extending over a length of operative coupling elements would become loosened, resulting in malaligned element arrays and in unsightly frayed sewn seams.